Hot melt adhesives are known, for instance, in the JP 2001787 describing tacky adhesive compositions for tapes comprising a block copolymer of a vinylaromatic hydrocarbon and a high vinyl polybutadiene block. The composition comprises a block copolymer, a tackifying resin and at least one phenol compound. The block copolymer is composed of at least one polymeric block mainly containing butadiene. It has a vinylaromatic hydrocarbon content of 10-36% by weight and the butadiene portions have a vinyl content of 15-55%.
The JP 63182386 discloses sticky block copolymer compositions containing a vinyl aromatic-butadiene block copolymer, a tackifying resin and a phenolic compound. The block copolymer is mainly composed of vinyl aromatic hydrocarbon and at least one polymer block composed of polybutadiene.
The EP-A-0 243 956 discloses an adhesive composition comprising a block copolymer containing at least one vinylaromatic hydrocarbon block and one butadiene containing block, wherein the relationship between the vinylaromatic hydrocarbon block and the 1,2-vinyl content in the butadiene portion is within a ratio between 40 and 70. In addition, the polymers that have been used have a melt flow rate of 5 g/10 min (200° C., 5 kg).
These hot melt compositions however do not have the same properties as those based on SIS in respect of the tack, adhesive strength creep resistance and treatment capacity at high temperature as well as high box closing properties.
The object of the invention is a hot melt adhesive composition having equal or better properties compared to prior art adhesives, especially the acrylic emulsion based adhesives while being cheaper than poly(styrene-isoprene-styrene) (SIS) based adhesives.
Poly(styrene-isoprene-styrene) polymers are currently rarely used in pressure sensitive adhesives despite their relative low cost. The main reason for this is their high viscosity and tendency to cross-link so that the processing step becomes a limiting factor. Surprisingly a new SBS polymer has been developed with molecular parameters suitable for to hot melt adhesive applications.